4.6.1 Internal Vibrators—The vibrator frequency shall be at
least 7000 vibrations per minute [115 Hz] while the vibrator is
operating in the concrete. The diameter of a round vibrator
shall be no more than one fourth the diameter of the cylinder
mold or one fourth the width of the beam or prism mold. Other
shaped vibrators shall have a perimeter equivalent to the
circumference of an appropriate round vibrator. The combined
length of the vibrator shaft and vibrating element shall exceed
the depth of the section being vibrated by at least 3 in. [75
mm].